Not going to deferred

I Have a deferred test on Friday for a class I know I have already failed no Matter what. My average was so low I would need a 90% to pass and I don’t want to go What can I say to the uc? Do they ask for like evidence for this? I was just going to say I’m sick. Don’t reply if you are just going to say “just go” I don’t want to I have accepted to take it next year where I think I will be more capable to do it.